1. Field of the Invention
The present invention relates to a sensor device and a display apparatus.
2. Background Art
In recent years, various types of proximity sensors have been developed. A proximity sensor is configured to detect proximity of an object. Examples of a sensing method performed by the proximity sensor include a resistive film method, infrared method, supersonic method, and capacitance method, each of which has a merit and a demerit. Examples of the proximity sensor are disclosed in Japanese Patent No. 3505961 and JP-A 2003-43078 (KOKAI).
The capacitance sensor is configured to detect proximity of an object to the sensor, by detecting a change in capacitance between the object and the sensor. The capacitance sensor has a feature that the sensor can detect proximity of the object even if the sensor is in no contact with the object, provided that the capacitance is within a detectable range. Recently, an optical sensor is popular as a non-contact type proximity sensor. However, the optical sensor has a demerit that the sensor is affected by ambient brightness. On the contrary, the capacitance sensor generally has no problem with ambient brightness.
The capacitance sensor detects proximity of an object by detecting a micro signal caused by movement of the object. Accordingly, in the capacitance sensor, it is important to realize a satisfactory S/N ratio for detecting the micro signal. In general, the capacitance sensor gives an AC signal to the object, and detects a change in the amplitude or phase of the AC signal resulting from a change in capacitance. In this case, to improve accuracy of detecting the object, it is necessary to take measures such as making the frequency of the AC signal variable, to realize a circuit system sensitive to a change in capacitance, and adding a time series detection unit (such as a counter) to a filtering unit. However, the former method may be restricted by frequency band, and the latter needs a timing circuit for synchronizing an input signal with an output signal.